| Cross Timbers | |
|---|---|
 The outline of the Cross Timbers as defined by theEPA | |
| Ecology | |
| Realm | Nearctic |
| Biome | Central forest-grasslands transition |
| Borders | |
| Geography | |
| Country | United States |
| States |
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The termCross Timbers, also known asEcoregion 29, Central Oklahoma/Texas Plains, is used to describe a strip of land in theUnited States that runs from southeasternKansas acrossCentral Oklahoma toCentral Texas.[1] Made up of a mix ofprairie,savanna, andwoodland,[2][3] it forms part of the boundary between the more heavily forested eastern country and the almost treelessGreat Plains,[2][3][4] and also marks the westernhabitat limit of manymammals andinsects.[2]
No major metropolitan areas lie wholly within the Cross Timbers, although roughly the western half of theDallas-Fort Worth Metroplex does, including the cities ofFort Worth,Denton,Arlington, andWeatherford.[3] The westernsuburbs of theTulsa metropolitan area and the northeastern suburbs of theOklahoma City metropolitan area also lie within this area.[2] The main highways that cross the region areI-35 andI-35W going north to south (although they tend to skirt the Cross Timbers' eastern fringe south of Fort Worth), and bothI-40 andI-44 going east to west. NumerousU.S. Highways also cross the area.[2][3] I-35 means a portion of Austin and Travis County is also included in the Cross Timbers.[1]
The Cross Timbers are defined by theUnited States Environmental Protection Agency as Ecoregion 29, aLevel III ecoregion. Some organizations and maps refer to the Cross Timbers ecoregion as the Central Oklahoma/Texas Plains.[4] The Cross Timbers are contained within theWWFcentral forest-grasslands transition ecoregion.
The woodland and savanna portions of the Cross Timbers are mainlypost oak andblackjack oak on coarse, sandy soils;[4]fire suppression in recent years has increased forest density and allowedeastern redcedar to invade as well. The short, stout oaks that grow in the Cross Timbers were not usable as timber, and those that were not cleared for farmland constitute one of the least disturbed forest types in the eastern United States, with some 890,000 acres (3,600 km2) ofold-growth forest scattered throughout the region.[5] These old-growth forests contain millions of post oak from 200 to 400 years old and red cedar over 500 years old.[5] The prairie portions are chieflytallgrass on finer, dry soils.[2] Overall, the Cross Timbers are not asarable as the surrounding ecoregions.[3] Today,land use is a mixture ofrangeland,pastures, andfarmland.[2] The area has also been an important site ofoil extraction for over 80 years.[3]
Geologically speaking, the Cross Timbers are underlain byPennsylvanian andCretaceous-erasandstone andlimestone that has been moderatelydissected, giving the region a gently to moderately rollingtopography,[3][4] including somecuestas.[2] Although localrelief is relatively low, it is generally greater than that in the surrounding ecoregions, although this is not the case with the Flint Hills in Kansas.[4]
Ecologically, the EPA includes the Cross Timbers as part of the vastGreat Plains, which comprise Level I Ecoregion 9.0, stretching fromcentral Alberta inCanada to northernMexico.[6] More specifically, the Cross Timbers fall into Level II Ecoregion 9.4, the smaller South Central Semi-Arid Plains.[7] In southern Oklahoma, the Cross Timbers are located on the very edge of the Great Plains, as they border directly parts of Level I Ecoregion 8.0, the Eastern Temperate Forests; elsewhere, the Cross Timbers are separated slightly from the Eastern Temperate Forests.[2] In turn, the Cross Timbers are themselves subdivided into nine Level IV Ecoregions:
This is a wide belt of land stretching from south-central Oklahoma into southeastern Kansas and is the only part of the Cross Timbers that extends into Kansas. In that state, it covers easternChautauqua andElk counties and smaller portions ofGreenwood,Woodson,Wilson, andMontgomery counties, while in Oklahoma, this region covers all ofSeminole,Pottawatomie, andOkfuskee counties, large parts ofOsage,Lincoln,Creek,Oklahoma,Cleveland,Pontotoc,Hughes,McIntosh, andOkmulgee counties, and smaller parts ofLogan,Garvin,Murray,Pawnee,Tulsa,Wagoner, andWashington counties. The towns ofSand Springs,Sapulpa,Ada, andShawnee, Oklahoma fall within this large area;Bartlesville andOkmulgee lie on the eastern edge.[2][4]
In Oklahoma, this belt of woodland covers all ofMarshall County and parts ofLove,Carter,Johnston, andBryan counties, but in Texas, this region exists as a long, very narrow strip of dense forest stretching from theRed River to just north ofWaco, Texas. It passes through northwesternGrayson County, easternCooke,Denton andTarrant counties, centralJohnson County, westernHill County, and northernMcLennan County. The city ofArlington, Texas lies within this zone, andDenton andCleburne are on its eastern edge.[2][8]
A much wider band than the Eastern Cross Timbers, the Western Cross Timbers band extends from far southern Oklahoma, including parts ofLove andCarter counties, into central Texas, where it covers large parts ofMontague,Young,Jack,Wise,Stephens,Palo Pinto,Parker,Eastland,Erath,Brown,San Saba, andMills counties, as well as smaller parts ofClay,Cooke,Callahan,Hood,Coleman, andMcCulloch counties. In Texas, this area includes the towns ofWeatherford andMineral Wells;Stephenville lies on the eastern fringe, whileBrownwood is on the western edge.[2][8]
The part of this region north ofI-20 is sometimes colloquially referred to as thePalo Pinto Mountains;[9][10][11] the hills are isolated, rugged, and scenic, with spectacularbluffs along theBrazos River as it flows through the region.[9][10][12]
Coal mining has historically been an important activity, asbituminous coal deposits are found throughout the region;[13] indeed, the town ofNewcastle in Young County was named after theEnglish city of the same name due to the coal connection.[14]
In the mid-to-late 19th century,ComancheIndians occupied this area, and it became a flash point for conflict between various groups of white settlers, the Comanche, and theU.S. Cavalry;FortsBelknap andRichardson were built in the area to protect this part of the frontier.[15]
Numerous roads cross this region, includingUS 70 in Oklahoma andI-20,I-30,US 67,US 81,US 82,US 180,US 183,US 281,US 287, andUS 380 in Texas.
A fairly narrow strip dividing the Eastern and Western Cross Timbers, the Grand Prairie differs inphysiography,topography, and land use from both of these, as it is much more nearly level and better suited toagriculture.[2] It includes a small part ofLove County, Oklahoma (the only part of this region outside of Texas) and passes south through westernCooke County, easternWise County, and westernDenton,Tarrant, andJohnson counties, and also includes parts ofParker,Erath,Hood,Somervell,Hill, andMcLennan counties. This region contains the cities ofFort Worth,Granbury andDenton, although Denton lies on the border with the Eastern Cross Timbers.[8]I-35 and I-35W cross north to south, whileUS 82,US 380,I-30,I-20,US 377, andUS 67 cross east to west;US 81 andUS 287 also cross southwest to northeast.
A broader, southern extension of the Grand Prairie, found only in Texas; it is underlain by limestone rather than sandstone, and serves as a physiological and vegetational transition to the Edwards Plateau, which it borders to the south. All ofHamilton andCoryell counties, large parts ofBell,Lampasas,Mills,Erath, andBosque counties, and smaller parts ofWilliamson,Burnet,Brown,Comanche,Hood,Somervell, andMcLennan counties, including the towns ofKilleen,Copperas Cove, andLampasas as well as theFort CavazosArmy base, fall within this region.[8] Among the few major roads that cross the Limestone Cut Plains areUS 281 north to south andUS 84 east to west.
This ecoregion exists as anenclave within the Western Cross Timbers, stretching from southernJack County, Texas across northwesternPalo Pinto County into easternStephens County, as well as tiny parts ofYoung andEastland counties. The region features a limestone substrate as opposed to sandstone, and has greater topographical relief and denser and different vegetation than other parts of the Cross Timbers. No towns of any size lie within this area, althoughPossum Kingdom Lake andState Park do;[8] the region is crossed byUS 180 andTexas State Highway 16.
Covering a fairly small area in south-central Oklahoma and underlain by a unique mosaic of several differentminerals, this region includes the town ofArdmore.[2]
An extension in two branches of the Cross Timbers into southwestern Oklahoma, this area features reduced tree density and height, but also small forests dominated bysugar maple,bur oak, andlive oak in deeper river canyons. The towns ofDuncan, Oklahoma andWalters, Oklahoma, lie in this region.[2]
TheArbuckle Mountains are located in a small area nestled in between regions 29g and h; it is made offolded, rather than dissected, limestone, sandstone, anddolomite, and features the greatest topographical relief of the entire Cross Timbers, though not the highest elevations. The landscape includes many caves,sinkholes,springs, and streams.[2]I-35 crosses this region north to south.
Part of the difference in the Cross Timbers region and the surrounding regions west (drier) and east (wetter) has to do with thedry line which separates humid air from theGulf of Mexico from the dry air of theLlano Estacado, theTexas Panhandle, and theHigh Plains.
The thick growth formed an almost impenetrable barrier for early American explorers and travelers.Washington Irving, in 1835, described it as "like struggling through forests of cast iron."[16]Rachel Plummer, while a captive of theComanche in 1836, described it as "a range of timber-land from the waters of Arkansas, bearing a southwest direction, crossing the False Ouachita, Red River, the heads of Sabine, Angelina, Natchitoches, Trinity, Brazos, Colorado...the range of timber is of an irregular width, say 5 to 35 miles wide...abounding with small prairies, skirted with timber of various kinds — oak, of every description, ash, elm, hickory, walnut and mulberry...the purest atmosphere I ever breathed was that of these regions."[17]Josiah Gregg described the Cross Timbers in 1845 as varying in width from five to thirty miles and attributed their denseness to the continual burning of the prairies.[18]
The Cross Timbers vary in width from five to thirty miles, and entirely cut off the communication betwixt the interior prairies and those of the great plains. They may be considered as the "fringe" of the great prairies, being a continuous brushy strip, composed of various kinds ofundergrowth; such as black-jack, post-oaks, and in some places hickory, elm, etc., intermixed with a very diminutive dwarf oak, called by the hunters, "shin-oak." Most of the timber appears to be kept small by the continual inroads of the "burning prairies;" for, being killed almost annually, it is constantly replaced by scions of undergrowth; so that it becomes more and more dense every reproduction. In some places, however, the oaks are of considerable size, and able to withstand the conflagrations. The Underwood is so matted in many places with grapevines, green-briars, etc., as to form almost impenetrable "roughs," which serve as hiding-places for wild beasts, as well as wild Indians; and would, in savage warfare, prove almost as formidable as the hammocks ofFlorida.
— Josiah Gregg
Robert Neighbors andRip Ford reached the "Cross Timbers, two parallel strips of timber region that ran down the middle of Texas", in 1849 while blazing an emigrant trail from Austin to El Paso.[19]: 116
